Thermal transport and mixed valence in ZrTe₃ doped with Hf and Se

Two-dimensional transition metal trichalcogenides (TMTCs) feature covalently bonded metal-chalcogen layers separated by the van der Waals (vdW) gap. Similar to dichalcogenides (TMDCs), TMTCs often host charge density waves (CDWs) and superconductivity, but unlike TMDCs, atomic chains in crystal structure give rise quasi one-dimensional (quasi 1D) conduction. ZrTe3 features CDW below TCDW = 63 K filamentary superconductivity 2 that can be enhanced pressure or chemical substitution. Here, we report presence of mixed valent Zr2+ Zr4+ atoms crystals are reduced doping ZrTe3−xSex Zr1−yHfyTe3. Superconductivity is via disorder Te2-Te3 associated with formation. Hf substitution on Zr site enhances due unperturbed chain periodicity electron-phonon coupling. Weak electronic correlations likely governed lattice contraction effects.